This invention relates to the casting of metal strip by continuous casting in a twin roll caster.
In a twin roll caster molten metal is introduced between a pair of counter-rotated horizontal casting rolls that are cooled so that metal shells solidify on the moving roll surfaces and are brought together at a nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow.
Further, the twin roll caster may be capable of continuously producing cast strip from molten steel through a sequence of ladles. Pouring the molten metal from the ladle into smaller vessels before flowing through the metal delivery nozzle enables the exchange of an empty ladle with a full ladle without disrupting the production of cast strip.
There are portions of the caster requiring service during operation. After being in operation for a duration, the texture on the casting rolls may diminish and lose its effectiveness, or other adverse conditions may develop, increasing or reducing the heat transfer through the casting roll surface. In this event, the flow of molten metal is halted, and the casting rolls may be replaced with a new or reconditioned pair of casting rolls. When the casting rolls are replaced, other portions of the metal delivery system may be replaced. Further, a scrap receptacle is positioned beneath the caster, and may fill up during operation of the caster. When the scrap receptacle fills, the full scrap receptacle may be moved away and an empty scrap receptacle put in place. The time it takes to replace these and other items cumulate in a change-over time. As the twin roll caster is not casting metal at least during portions of the change-over time, it is desired to reduce the change-over time.
An apparatus is disclosed for continuously casting thin steel strip comprising:                (a) a pair of counter-rotatable casting rolls having casting surfaces laterally positioned to form a nip there between through which thin cast strip can be cast, and on which a casting pool of molten metal can be formed supported on the casting surfaces above the nip;        (b) the casting rolls mounted in a roll cassette capable of being transferred from a set up station to a casting position through a transfer station, where at the set up station the casting rolls mounted in the roll cassette are capable of being prepared for casting, at the transfer station roll cassettes with the mounted casting rolls are capable of being exchanged, and in the casting position the casting rolls mounted in the roll cassette are operational in the caster; and        (c) casting roll guides adapted to enable movement of the casting rolls mounted in the roll cassette between the set up station and the transfer station and between the transfer station and the casting position.        
The casting roll guides may be adapted to enable movement of the casting rolls mounted in the roll cassette from the set up station to the casting position through the transfer station at substantially the same elevation. Alternately or in addition, the first and second rails may be adapted to enable movement of the casting rolls mounted in the roll cassette between the set up station and the transfer station at a different elevation than moving the casting rolls from the transfer stations to the casting position.
The casting roll guides may comprise rails on which the casting rolls mounted in the roll cassette are capable of being moved between the set up station and the casting position through the transfer station. First rails extend between the set up station to the transfer station, second rails extend between the transfer station to the casting position, and both first and second rails are capable of being aligned with rails on a turntable of the transfer station such that the turntable may be turned to exchange casting rolls mounted in roll cassettes between the first rails and the second rails. The first and second rails may be adapted to enable movement of the casting rolls mounted in the roll cassette from the set up station to the casting position through the transfer station at substantially the same elevation or at different elevations.
At the casting position, the casting rolls are moved into operating position for casting of thin strip. This movement of the casting rolls into operating position may be by raising, lowering or lateral motion of the casting rolls. This movement of the casting rolls into operating position may be by movement of the casting rolls and the roll cassette as a unit, or by moving the casting rolls separate from at least part of roll cassette. This movement will generally depend on the particular embodiment desired, but the movement will be generally as little as practical so as to reduce motion and time in positioning the casting rolls in operating position. The operating position may be as the casting rolls reach the casting position without change in elevation or lateral motion.
The apparatus for continuously casting thin steel strip may include an enclosure capable of supporting a protective atmosphere immediately beneath the casting rolls in the casting position; and an upper cover capable of moving between a closed position covering an upper portion of the enclosure and a retracted position enabling cast strip to be cast downwardly from the nip into the enclosure. Guides, such as a pair of rails, may be provided adapted to enable movement of the upper cover between the closed position and the retracted position. A plurality of actuators may be selected from the group consisting of servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators capable of moving the upper cover along the guides between the closed position and the retracted position.
The apparatus may include an upper collar portion movable between an extended position in sealing engagement to support a protective atmosphere immediately beneath the casting rolls in the casting position and an open position enabling the upper cover to move into its closed position. A plurality of actuators selected from the group consisting of servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators are provided capable of moving the upper collar between the extended position and the open position.
In addition, a housing portion may be positioned adjacent the casting rolls capable of supporting a protective atmosphere immediately beneath the casting rolls in the casting position, and a knife seal positioned adjacent each casting roll and adjoining the housing portion and forming a partial closure between the housing portion and the rotating casting rolls.
The apparatus for continuously casting steel strip may further comprise at least one scrap receptacle capable of being positioned beneath the casting rolls in the casting position and movable in either direction away from the casting position on a scrap receptacle guide to discharge stations, each scrap receptacle capable of attaching with the enclosure capable of supporting a protective atmosphere immediately beneath the casting rolls in the casting position. The scrap receptacle guide may comprise rails extending in opposite directions from the casting position, the rails capable of supporting at least two scrap receptacles movable along the rails from the casting position to the discharge stations.
Further, the apparatus for continuously casting steel strip may include a rim portion capable of sealingly engaging an upper portion of the scrap receptacle positioned beneath the casting position. The apparatus may further include a lower plate operatively positioned within the enclosure capable of closing a lower portion of the enclosure when the rim portion is disengaged from the scrap receptacle. The lower plate may have two portions pivotably mounted to move into a closed position. A plurality of actuators selected from the group consisting of servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators may be provided capable of moving the lower plate between the closed position and a retracted position.
The apparatus for continuously casting thin steel strip may further comprise:                (d) a movable tundish capable of being transferred from a heating station to the casting position and capable of receiving molten metal and transferring the molten metal to the casting pool through a distributor and a core nozzle when in the casting position, and        (e) a tundish guide adapted to enable movement of the movable tundish from the heating station where the movable tundish is capable of being heated to an operative temperature to the casting position.        
The tundish guide may comprise rails extending between the heating station and the casting position. Further, the movable tundish may be capable of being movable in either direction away from the casting position via the tundish guide.
Additionally, a loading device may be provided capable of moving the distributor from a stand-by position to the casting position. At least a portion of the loading device may be overhead from the elevation of the distributor positioned in the casting position. The loading device may be a loading arm movable with the movable tundish on the tundish guide and capable of lifting the distributor from the stand-by position and placing the distributor over the casting rolls in the casting position.
A method of continuously casting steel strip is disclosed comprising the steps of:                (a) assembling a first pair of counter-rotatable casting rolls mounted in a roll cassette having casting surfaces laterally positioned to form a nip there between through which thin cast strip can be cast, and on which a casting pool of molten metal may be formed supported on the casting surfaces above the nip,        (b) preparing the first casting rolls mounted in a roll cassette for casting at a set up station;        (c) moving the first casting rolls mounted in a roll cassette to a transfer station;        (d) moving the first casting rolls mounted in a roll cassette from the transfer station to casting position where the pair of counter-rotatable casting rolls is positioned for casting thin strip.        
The method of continuously casting steel strip may further comprise the steps:                (e) exchanging at the transfer station the first casting rolls mounted in a roll cassette with a second casting rolls mounted in a second roll cassette, and        (f) moving the second casting rolls mounted in a second roll cassette from the transfer station to the set up station where the second casting rolls can be changed (i.e., placed, repaired or refurbished).        
In the method of continuously casting steel strip, the moving of first and second roll cassettes with casting rolls mounted thereon between the set up station and the casting position may be done on rails, with first rails extending between the set up station and the transfer station, second rails extending between the transfer station and the casting position, and the first and second rails capable of being aligned with rails on a turntable at the transfer station such that the turntable may be turned to exchange casting rolls mounted in roll cassettes between the first set of rails and the second set of rails. The first and second casting rolls mounted in roll cassettes can be moved between the set up station and the casting position through the transfer station at substantially the same elevation or different elevations.
A method of continuously casting steel strip is disclosed using a pair of counter-rotatable casting rolls mounted in a roll cassette having casting surfaces laterally positioned to form a nip there between through which thin cast strip can be cast, and on which a casting pool of molten metal can be supported on the casting surfaces above the nip, the improvement providing for rapid exchange of casting rolls comprising the steps of:                (a) providing an enclosure capable of supporting a protective atmosphere immediately beneath the casting rolls in the casting position having an upper cover capable of moving between a retracted position and a closed position beneath the casting rolls and covering the enclosure;        (b) moving the upper cover to the retracted position enabling cast strip to be cast downwardly from the nip into the enclosure; and        (c) moving the upper cover to the closed position retaining the protective atmosphere in the enclosure and enabling the casting rolls to be removed from the casting position.        
The method of continuously casting steel strip may comprise in addition locating at least one scrap receptacle capable of being positioned beneath the casting rolls and the enclosure in the casting position and movable in either direction away from the casting position by scrap receptacle guides to discharge stations, each scrap receptacle capable of attaching with the enclosure capable of supporting a protective atmosphere immediately beneath the casting rolls in the casting position.
The method may include engaging an upper collar portion adjacent to the casting rolls to support the protective atmosphere in the enclosure beneath the casting rolls, and disengaging the upper collar portion to enable the upper cover to be moved into the closed position. The method may also include engaging a seal between a scrap receptacle and the enclosure to support the protective atmosphere in the enclosure beneath the casting rolls. Additionally, the method may include the step of closing the lower portion of the enclosure when the seal is disengaged from the scrap receptacle to enable casting to continue during change of the scrap receptacle, if desired.
The method of continuously casting steel strip may also include positioning rails to form the scrap receptacle guides in opposite directions from the casting position, the rails capable of supporting at least two scrap receptacles movable along the rails from the casting position to the discharge stations away from the caster, and may include sealing an upper portion of a scrap receptacle in sealing engagement with an enclosure supporting a protective atmosphere beneath the casting position.
The method of continuously casting steel strip may comprise in addition, moving a movable tundish, which is capable of receiving molten metal and transferring the molten metal to the casting pool through a distributor and a core nozzle, from a heating station to a casting position via a tundish guide elevated above the movement of the first casting rolls mounted in a roll cassette from the heating station to the casting position.
The guide may comprise rails extending between the heating station and the casting position.
The method of continuously casting steel strip may include providing a loading device with the movable tundish capable of moving the distributor from a stand-by position and placing the distributor over the casting rolls in the casting position, the loading device being elevated above the movement of the first casting roll mounted in a roll cassette; advancing the movable tundish from the heating station to the casting position; and moving the distributor from the stand-by position and placing the distributor over the casting rolls in the casting position.
Alternately, a method of continuously casting steel strip may comprise steps of:                (a) providing rails positioned beneath a casting position and extending in opposite directions there from to discharge stations;        (b) supporting first and second scrap receptacles movable along the rails;        (c) sealingly engaging the first scrap receptacle with an enclosure enabling support of a protective atmosphere beneath a pair of casting rolls;        (d) disengaging the seal between the first scrap receptacle and the enclosure and moving the first scrap receptacle along the rails in a direction away from the second scrap receptacle to a discharge station; and        (e) moving the second scrap receptacle into the casting position and sealingly engaging the second scrap receptacle and the enclosure.        
The method may include filling the second scrap receptacle with a desired protective gas before moving the second scrap receptacle into the casting position.
The method of continuously casting steel strip may further comprise:                (f) preparing the first casting rolls mounted in a roll cassette for casting at a set up station;        (g) moving the first casting rolls mounted in a roll cassette from the set up station to a transfer station;        (h) exchanging at the transfer station the first casting rolls mounted in a roll cassette with second casting rolls mounted in a second roll cassette;        (i) moving the first casting rolls mounted in a roll cassette from the transfer station to the casting position where the first pair of counter-rotatable casting rolls are positioned for casting thin strip; and        (j) moving the second casting rolls mounted in a second roll cassette from the transfer station to the set up station where the second casting rolls can be changed.        
The method of continuously casting thin steel strip may comprise in addition, moving a movable tundish, which is capable of receiving molten metal and transferring the molten metal to the casting pool through a distributor and a core nozzle, from a heating station to a casting position by a tundish guide elevated above the movement of the first and second casting rolls in roll cassettes from the transfer station to the casting position.
The tundish guide may comprise rails extending between the heating station and the casting position. The method may further include providing a loading device with the movable tundish capable of moving the distributor from a stand-by position and placing the distributor over the casting rolls in the casting position, the loading device elevated above the movement of the first and second casting rolls; advancing the movable tundish from the heating station to the casting position; and positioning the distributor from a stand-by position and placing the distributor over the casting rolls in the casting position.